Unending search for elusive dark matter sets a new record

In our quest to understand the universe, one mysterious substance has consistently evaded direct detectors — dark matter.

Despite being practically invisible, it carries the weight of 85% of the universe’s mass, influencing the formation of galaxies and the universe’s overall structure.

But the veil of this elusive entity may be lifting, thanks to the relentless efforts of dedicated scientists and the world’s most sensitive dark matter detector.

Dark matter detector at LUX-ZEPLIN (LZ)

This mission is led by stellar personnel from the LUX-ZEPLIN (LZ) collaboration. Spearheading the project from a cavern deep beneath the earth’s surface at the Sanford Underground Research Facility in South Dakota is Professor Chamkaur Ghag from University College London (UCL).

He, along with over 250 scientists from around the globe, is on the hunt for weakly interacting massive particles, or WIMPs, a prime candidate for dark matter.

“These are new world-leading constraints by a sizable margin on dark matter and WIMPs,” explained Ghag.

He noted that the detector and analysis techniques are performing even better than the collaboration expected.

“If WIMPs had been within the region we searched, we’d have been able to robustly say something about them. We know we have the sensitivity and tools to see whether they’re there as we search lower energies and accrue the bulk of this experiment’s lifetime,” Ghag continued.

Digging deep for invisible treasure

The latest results from the LZ experiment are a watershed moment in our search for WIMPs. Using data collected over 280 days, the team scoured the darkest recesses of the universe, only to come back empty-handed.

There was no evidence of WIMPs above a mass of 9 gigaelectronvolts per square centimeter (GeV/c²). But don’t be mistaken, this isn’t bad news. The findings help researchers rule out a swath of potential WIMP models.

As Scott Kravitz, LZ’s deputy physics coordinator from the University of Texas at Austin, compares, the pursuit for dark matter is reminiscent of a treasure hunt, with LZ digging almost five times deeper than previous efforts.

“If you think of the search for dark matter like looking for buried treasure, we’ve dug almost five times deeper than anyone else has in the past,” Kravitz noted. “That’s something you don’t do with a million shovels — you do it by inventing a new tool.”

LZ dark matter detector is a tech marvel

The profound sensitivity of LZ lies at the intersection of innovative analysis techniques and advanced technology. The detector is a modern marvel, designed to minimize external noise and track particle interactions.

Furthermore, the LZ team uses an intriguing “salting” approach, intermixing fake WIMP signals within the data, to safeguard against bias.

This ensures the data’s integrity, as Scott Haselschwardt, the LZ physics coordinator from the University of Michigan, emphasizes the need to keep bias out of the equation when entering a new realm of analysis.

“We’re pushing the boundary into a regime where people have not looked for dark matter before,” said Haselschwardt. “There’s a human tendency to want to see patterns in data, so it’s really important when you enter this new regime that no bias wanders in. If you make a discovery, you want to get it right.” 

Dark matter in the grand scheme

Despite its phantom presence, dark matter plays a vital role in the stability and formation of galaxies. Without it, the universe would be unrecognizable.

While LZ’s advancements may exclude certain WIMP possibilities, they also pave the way for further inquiries. Apart from the WIMP search, LZ’s detector also scans for other exotic physics phenomena.

Amy Cottle, UCL assistant professor and WIMP search effort leader, is excited for what’s next.

“We’ve demonstrated how strong we are as a WIMP search machine, and we’re going to keep running and getting even better — but there’s lots of other things we can do with this detector,” Cottle enthused.

“The next stage is using these data to look at other interesting and rare physics processes, like rare decays of xenon atoms, neutrinoless double beta decay, boron-8 neutrinos from the sun, and other beyond-the-Standard-Model physics. And this is in addition to probing some of the most interesting and previously inaccessible dark matter models from the last 20 years,” she concluded.

Sweat, grind, and more research

LZ’s journey is a stirring tale of international cooperation. With contributors from across the globe, the project harnesses a pool of multifaceted expertise.

The team is also planning upgrades to the LZ detector and eyeing a next-generation dark matter detector, the XLZD.

Scott Kravitz sums up the spirit and aspiration of this ambitious venture, stating, “Our ability to search for dark matter is improving at a rate faster than Moore’s Law. Just wait until you see what comes next.”

The pursuit of dark matter is much like climbing an endless mountain; we may not have reached the peak yet, but each ascent takes us a step closer. The LZ team’s tireless endeavors have narrowed the path forward, paving the way for future revelations.

Who knows, the day may not be too far when we finally unveil the secrets of dark matter, transforming it from an enigma to a cornerstone of our cosmic comprehension. Until then, as we delve deeper and more precisely into the mysteries of the universe, the exhilarating odyssey continues.

The new results were presented at two physics conferences on August 26: TeV Particle Astrophysics 2024 in Chicago, Illinois, and LIDINE 2024 in São Paulo, Brazil. A scientific paper will be published in the coming weeks.

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